FeatureMatching Combining Variable Velocity Model with Reverse Optical Flow

The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an inaccurate pose estimation or failed tracking.To address the challenge above,a new method of feature point matching is proposed in this paper,which combines the variable velocity model with the reverse optical flow method.First,the constant velocity model is extended to a new variable velocity model,and the expanded variable velocity model is used to provide the initial pixel shifting for the reverse optical flow method.Then the search range of feature points is accurately determined according to the results of the reverse optical flow method,thereby improving the accuracy and reliability of feature matching,with strengthened interframe tracking effects.Finally,we tested on TUM data set based on the RGB-D camera.Experimental results show that this method can reduce the probability of tracking failure and improve localization accuracy on SLAM(Simultaneous Localization and Mapping)systems.Compared with the traditional ORB-SLAM2,the test error of this method on each sequence in the TUM data set is significantly reduced,and the root mean square error is only 63.8%of the original system under the optimal condition.

Vertical distribution of soil moisture and surface sandy soil wind erosion for different types of sand dune on the southeastern margin of the Mu Us Sandy Land,China

Soil moisture is a critical state affecting a variety of land surface and subsurface processes. We report investigation results of the factors controlling vertical variation of soil moisture and sand transport rate of three types of dunes on the south- eastern margin of the Mu Us Sandy Land. Samples were taken from holes drilled to a depth of 4 m at different topographic sites on the dunes, and were analyzed for soil moisture, grain-size distribution and surface sediment discharge. The results show that： （1） The average soil moisture varies in different types of dunes, with the following sequences ordered from highest to lowest： in the shrubs-covered dunes and the trees-covered dunes the sequence is from inter-dunes lowland to windward slope to leeward slope. The average moisture in the bare-migratory sand dunes is sequenced from inter-dunes lowland to leeward slope to windward slope. （2） Vegetation form and surface coverage affect the range of soil moisture of different types of dunes in the same topographic position. The coefficient of variation of soil moisture for shrubs-covered dunes is higher than that of other types of dune. （3） The effect of shrubs on dune soil moisture is explained in terms of the greater ability of shrubs to trap fine-grained atmospheric dust and hold moisture. （4） The estimated sand transport rates over sand dunes with sparse shrubs are less than those over bare-migratory dunes or sand dunes with sparse trees, indicating that shrubs are more effective in inhibiting wind erosion in the sandy land area.

Angiopoietin-1 mRNA expression in estradiol-treated ovariectomized rats with focal cerebral ischemia after reperfusion

BACKGROUND： Epidemiologic studies have indicated that the incidence of stroke in premenopausal females is lower than in males at the same age, but it significantly rises in postmenopansal females. Estrogen is used clinically to alleviate injury caused by cerebral ischemia, it has been hypothesized that the neuroprotective role of estrogen relates to angiopoietin （Angpt）, which plays an important role in vascularization, vascular remodeling and maturation. OBJECTIVE： To observe and validate the effect of estradiol on angiopoietin-1 （Angptl） mRNA expression in ovariectomized rats with focal cerebral ischemia after reperfusion, so as to explore the molecular mechanisms of estradiol-mediated protection from cerebral ischemic damage. DESIGN, TIME AND SETTING： Randomized, controlled, molecular biology, prospective animal study. The experiment was performed at the Central Laboratory of Chongqing Medical University from September to December 2005. MATERIALS： Fifty healthy female wild type （WT） rats aged 6 months and fifty female rats aged 6 months with knockout of the estrogen-alpha receptor gene （ERKO）. METHODS： WT rats and ERKO rats were divided into estradiol and control groups （n = 25）, and injected intramuscularly with estradiol benzoate （100μg/kg per day） or corn oil （l mL/kg per day） for 7 days, 30 days after bilateral ovariectomy. Rat models of cerebral ischemia/reperfusion were established with the middle cerebral artery occlusion method. After 30 minutes of middle cerebral artery occlusion, rats from the estradiol and control groups were injected intramuscularly with estradiol benzoate or corn oil at the above dose. MAIN OUTCOME MEASURES： We used radio-immunity analysis and laser-Doppler flowmetry to measure plasma estradiol levels and changes in cerebral blood flow. We used immunohistochemical staining of CD34 epitopes to measure changes in the capillary density in brain following cerebral iscbemia/reperfusion, and quantitative RT-PCR analysis to assess mRNA expression levels of Angptl, Angpt2, Tie2, vascular endothelial growth factor （Vegf）, VegfR1, and Veg, fR2. RESULTS： In WT ovariectomized rats treated with estradiol, the change in cerebral blood flow following cerebral ischemia/reperfusion, capillary density in the basal nuclei and parietal lobe cortex and Angptl mRNA level were significantly higher than in the control group （P 〈 0.01 ）. We did not identify any such changes in ERKO rats treated with estradiol. In addition, the plasma estradiol levels in WT and ERKO ovariectomized rats treated with estradiol were remarkably higher than in their corresponding control groups （P 〈 0.01）. CONCLUSION： Angptl is a critical factor in many processes during the repair of cerebral ischemia/reperfusion injury. For example, it confers estrogen-mediated protection, restoration of cerebral blood flow and increases in brain capillary density. It is emerging as an important molecule for estradiol-mediated neuroprotection.

Paleoclimatic application of spectral parameters to the eolian red clay of the Jianzha Basin,northeastern margin of the Tibetan Plateau

Reflectance spectroscopy is rapid,inexpensive,and non-destructive and can provide important information about the mineralogy of rocks and sediments.We measured the reflectance spectroscopy of Miocene red clay deposits on the northeastern margin of the Tibetan Plateau,with the aim of developing a rapid methodology for detecting paleoclimatic changes.We obtained visible/near-infrared(VNIR)and short-wave infrared(SWIR)spectroscopy data from the red clay in the Jianzha Basin,and analyzed their relationship with independent paleoclimatic records,including mineral contents and environmental magnetic parameters.The results show that the VNIR parameters,including D500,D900,R500,and R900(where D and R represent the depth and reflectance of the absorption peaks around 500 and 900 nm,respectively)are temperature-sensitive and correlated with the magnetic susceptibility,frequency-dependent magnetic susceptibility,and the marine δ^(18)O record.The results of frequency-domain analysis of the VNIR parameters show that they reflect climate change on orbital timescales.SWIR parameters,such as AS1400,D1400/D1900 and D1900(where AS represents the asymmetry of the absorption peaks around1400 nm),are correlated with the illite and montmorillonite content,and they are sensitive to the weathering intensity.The spectral parameters of the eolian red clay in the Jianzha Basin reflect regional climatic changes caused by the uplift of the Tibetan Plateau at~8.5 Ma and global climatic cooling at~7.2 Ma,and thus they are applicable as both regional and global paleoenvironmental indicators.

Oxidation Resistance of In Situ Reaction/Hot Pressing Synthesized Ti_(2)AlC-20%TiB_(2) Composite at 600-900℃in Air

The oxidation behavior and kinetics of Ti_(2)AlC-20vol.%TiB_(2) composite at 600-900℃ in air were investigated.The results showed that the oxidation kinetics of the composite followed a logarithmic law within the given temperature range,which indicated that the composites had excellent oxidation resistance.The selective oxidation of Al in Ti_(2)AlC was greatly enhanced,which facilitated the formation of a continuous and dense protective layer of Al_(2)O_(3).Meanwhile,the existence of molten B_(2)O_(3) inhibited the outward diffusion of Ti and inward diffusion of oxygen,which prevented the growth of anatase TiO_(2) at 600℃ and rutile TiO_(2) at 700-900℃.Therefore,the incorporation of TiB_(2) completely inhibited the abnormally rapid oxidation of bulk Ti_(2)AlC at 600℃ and improved its oxidation resistance at 700-900℃.

微小RNA在增生性瘢痕中的作用及其机制研究进展

增生性瘢痕(HS)影响患者功能与美观,给患者带来沉重的心理负担,但其具体的分子生物学水平发病机制尚不明确,因此该病仍然是临床难防难治疾病之一。微小RNA(miR)是一类具有调节基因表达作用的单链内源性非编码RNA。miR在HS的成纤维细胞内的异常转录可影响下游信号通路或蛋白的转导与表达,对miR及其下游信号通路、蛋白的探究有助于深入了解瘢痕增生的发生和发展机制。该文总结并分析近年来miR与多种信号通路如何参与HS的形成与发展,并进一步概述miR与HS中靶基因之间的相互作用。

A novel medium-entropy(TiVNb)_(2)AlC MAX phase:Fabrication,microstructure,and properties

Medium-or high-entropy materials have great potential for applications due to their diverse compo-sitions and unexpected physicochemical properties.Herein,a novel medium-entropy(TiVNb)_(2)AlC was synthesized via hot pressing at 1400℃from three individual M_(2)AlC(M=Ti,V,Nb)MAX phases.The microstructure of(TiVNb)_(2)AlC was characterized from the microscale to the atomic scale by scanning electron microscope microscopy(SEM),scanning transmission electron microscopy(STEM),and energy dispersive spectroscopy(EDS).The results showed that Ti,V,and Nb atoms were fully solid-soluble in the M-sites of the M_(2)AlC MAX phase.Compared with three individual MAX phases,the thermal conduc-tivity of(TiVNb)_(2)AlC was reduced greatly in the temperature range of 293-1473 K,and its mechanical properties(including Young’s modulus,Vickers hardness,and bending strength)were all increased due to the solid solution strengthening and electronic mechanism.

Microstructure and mechanical properties of short-carbon-fiber/Ti_(3)SiC_(2) composites

Short-carbon-fibers(C_(sf))reinforced Ti_(3)SiC_(2) matrix composites(C_(sf)/Ti_(3)SiC_(2),the C_(sf) content was 0 vol%,2 vol%,5 vol%,and 10 vol%)were fabricated by spark plasma sintering(SPS)using Ti_(3)SiC_(2) powders and C_(sf) as starting materials at 1300℃.The effects of C_(sf) addition on the phase compositions,microstructures,and mechanical properties(including hardness,flexural strength(σ_(f)),and KIC)of C_(sf)/Ti_(3)SiC_(2) composites were investigated.The C_(sf),with bi-layered transition layers,i.e.,T_(IC) and SiC layers,were homogeneously distributed in the as-prepared C_(sf)/Ti_(3)SiC_(2) composites.With the increase of C_(sf) content,the K_(IC) of C_(sf)/Ti_(3)SiC_(2) composites increased,but the σ_(f) decreased,and the Vickers hardness decreased initially and then increased steadily when the C_(sf) content was higher than 2 vol%.These changed performances(hardness,σ_(f),and K_(IC))could be attributed to the introduction of C_(sf) and the formation of stronger interfacial phases.

Two 2D uranyl coordination complexes showing effective photocatalytic degradation of Rhodamine B and mechanism study

Two new hydrostable two-dimensional(2 D) uranyl coordination complexes [(UO_(2))_(5)(μ_(3)-O)_(2)(nbca)_(2)].7 H_(2)O(1) and [(UO_(2))_(3)(nbca)_(2)(H_(2)O)_(3)]·2 H_(2)O(2)(H_(3) nbca=5-nitro-1,2,3-benzenetricarboxylic acid) were hydrothermal synthesized.Single-crystal structural refinements reveal that both of the two complexes were formed by the packing of 2D uranyl coordination sheets via the hydrogen bonds.The nbca ligand coordinating to the uranyl polyhedron centers constructed the 2D sheets.There are UO8 hexagonal bipyramids and UO7 pentagonal bipyramids in 1 while only U07 pentagonal bipyramids in 2.Photocatalytic degradation of rhodamine B(RhB) in aqueous solution was studied.Complex 2 possesses better performance than 1 with 96.2 % of the RhB was degraded in only 60 min.Mechanism studies reveal that the dissolved oxygens are essential to the RhB degradation.The photocurrent density of 2 is more stable than that of 1,which indicating the stronger ability to separate photoexcited electrons and hole pairs of 2.

Microcystin-degrading bacteria affect mcy D expression and microcystin synthesis in Microcystis spp

Cyanobacterial blooms occur increasingly often and cause ecological,economic and human health problems worldwide.Microcystins（MCs）are the dominant toxins produced by cyanobacteria and are implicated in epidemic disease and environmental problems.Extensive research has been reported on the various regulating factors,e.g.,light,temperature,nutrients such as nitrogen and phosphorus,p H,iron,xenobiotics,and predators,that influence microcystin（MC）synthesis,but little is known about the effects of cyanobacteria-associated bacteria on MC synthesis.A considerable number of studies have focused on interactions between Microcystis species and their associated bacteria.In this study,we evaluated the effects of MC-degrading bacteria（MCDB）on MC synthesis gene mcy D expression and MC synthesis in axenic strain PCC7806,non-axenic strain FACHB905,and colony strain FACHB1325 of Microcystis by quantitative real-time polymerase chain reaction（RT-PCR）assay and enzyme-linked immunosorbent assay（ELISA）.We demonstrate for the first time that MCDB can induce and up-regulate the MC production and transcriptional response of the mcy D gene of toxic Microcystis.On day 4 of the culturing experiment,the intracellular MC concentration and transcriptional response of mcy D of FACHB1325 were up-regulated 1.9 and 5.3-fold over that of the control,and for FACHB905 were up-regulated 1.8 and 4.2-fold over that of the control,respectively.On day 10,the transcriptional response of mcy D was up-regulated 21.3-fold in PCC7806.These results indicate that there are interactions between toxic Microcystis and MCDB,and MCDB may play a role in regulating mcy D expression in toxic Microcystis.